Located at the lowest part of the brainstem and in front of the cerebellum, the long stem-like continuation of the spinal cord is called medulla oblongata (or: medulla). The medulla oblongata is the control center of the heart, lung, and digestive functions of our body (i.e. vasomotor respiration and digestion control).
What Is the Function of the Medulla Oblongata?
The medulla oblongata controls and regulates the autonomic activities of the heart, lung, and digestive system structures, such as breathing, heartbeat, vomiting, coughing, digestion, the sleep cycles (falling asleep and waking up), sneezing, swallowing, and blood pressure.
Furthermore, this brain structure is responsible for the relay of signals of the neuron cells between the brain and the spinal cord, functioning as a neural pathway. The medulla oblongata also regulates, controls, and coordinates various body movements via the numerous nuclei of the cranial nerves, located in this brain structure.
How Does the Medulla Oblongata Control Breathing?
The main function of the medulla oblongata is to control the muscles that aid our breathing by sending signals from the corresponding brain region to the ventral respiratory group of neurons (responsible for the rhythm of our breathing). In this way, breathing becomes an automatic action of the lungs produced by a group of neurons in the brain stem.
In addition, the medulla oblongata also controls all involuntary movements of the body, such as the movement of the shoulders, movements of the head, the movement of the oral tract during speaking, the movement of the ingested matter in the digestive system of the body, etc.
Anatomy and Structure of the Medulla Oblongata
The following exploration of the medulla oblongata refers to its external features, as well as its internal anatomy.
External Anatomy of the Medulla Oblongata
The lowest part of the brain stem is comprised of two major areas: the anterior (frontal) surface and the posterior (back) surface.
The Anterior Surface of the Medulla Oblongata
The front part of the medulla oblongata is comprised of the following structures:
- The anterior median fissure
- The ventrolateral sulcus
- The posterolateral sulcus
- The pyramids of the medulla oblongata
- The olives of the medulla oblongata
The Pyramids of the Medulla Oblongata
To begin with, the pyramidal tracts are located in the cerebral cortex. By providing a passage for the motor fibers to reach the spinal cord and brainstem, they participate in the voluntary control of the musculature of the body and face.
The name of the pyramidal tracts originates from the medullary pyramids of the medulla oblongata. Namely, the pyramids are paired swellings that are located between the anterior median fissure and the ventrolateral sulcus.
The pyramids are home to the arcuate nuclei. These nuclei are housed on the anterior surface of the pyramids of the medulla oblongata. They receive neuron fibers from the cerebral cortex and send their fibers via the anterior external arcuate fibers to the cerebellum.
The Olives of the Medulla Oblongata
The olives are another pair of swellings located on the side portion to the pyramids – between the ventrolateral and posterolateral sulcus. They contain the olivary nuclei.
The olives of medulla oblongata consist of two nuclei:
- The inferior olivary nucleus – This nucleus is composed of 3 sub-nuclei: the primary olivary nucleus, the medial accessory olivary nucleus, and the dorsal accessory olivary nucleus. The inferior olivary nucleus participates in the cerebellar motor-learning and function.
- The superior olivary nucleus – This nucleus is also regarded as a part of the pons, which means it’s also a part of the auditory system and supports the perception of sound.
The Posterior Surface of the Medulla Oblongata
The back part of the medulla oblongata is comprised of the following structures:
- The posterior median sulcus
- The fasciculus gracilis
- The fasciculus cuneatus
- The posterior intermediate sulcus
Internal Anatomy of the Medulla Oblongata
Internally, the medulla oblongata is divided into two regions:
- The open medulla oblongata
- The closed medulla oblongata
When the cavities that contain cerebrospinal fluid are surrounded by the medulla oblongata, we refer to the medulla as closed. If not, we can label the medulla as open. The medulla becomes open when the central canal opens into the fourth ventricle.
The internal view of the medulla displays 3 levels of decussation, i.e. the cross point of the neuronal fibers that branch from one side of a structure to the other:
- Level of decussation of the pyramids of the medulla oblongata – This motor neuron decussation occurs at the midline crossing point between the motor fibers from the medullary pyramids. From here, the neuron fibers continue to branch into the spinal cord.
- Level of decussation of the medial lemniscus – The sensory decussation occurs at the level of the medial lemniscus (a large ascending set of neuronal axons that decussate in the brainstem).
- Level of the olives of the medulla oblongata – The large inferior olivary nucleus is responsible for the external expansion of the olives of the medulla oblongata.
What Is the Difference Between Decussation and Chiasma?
While the term decussation refers to a crossing of the neuron fibers within the central nervous system, other types of crossings in the peripheral nervous system are labeled as a chiasma (for instance, the optic chiasm).
What Are the Nuclei of the Medulla Oblongata?
The medulla oblongata contains the cardiac, respiratory, vomiting, and vasomotor centers of the brain, hence it controls and regulates the autonomic functions of breathing, heart rate, blood pressure, as well as the sleep-wake cycle:
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- The nuclei of the abducens nerve (CN VI)
- The nuclei of the hypoglossal nerve (CN XII)
- The nuclei of the glossopharyngeal nerve (CN IX)
- The nuclei of the vagus nerve (CN X)
- The nuclei of the accessory nerve (CN XI)
What Happens If the Medulla Oblongata Becomes Dysfunctional?
If the medulla oblongata has a lesion or suffers an injury, that can lead to several medical conditions and disorders:
- Paralysis
- Loss of the sense of touch
- Vertigo
- Difficulty with swallowing
- Difficulty vomiting
- Loss of sense of pain
- Loss of coordination of movements
- Facial numbness
- Lateral medullary syndrome of Wallenberg
- Medial medullary syndrome
Most of the pathological concerns of the medulla oblongata result from compression or destruction of the tracts that traverse the conduit and the nuclei located in this structure of the brain. An example of a tumor of the medulla oblongata is a medulloblastoma – a primary central nervous system tumor.
Fun Facts
Did you know?
- The brain stem is the main “communicator” of the brain – all brain parts send their information through this part of the brain in order to reach, control, and regulate the parts of our body. In this manner, the brain stem serves as a kind of “bridge” between the head and the body.
- Despite being small in size, the brain stem is so powerful that it supports breathing, as one of the most vitally important processes of our body. In addition, it incorporates all of the automatic body processes, such as swallowing, eye-movement, chewing, etc.
- The medulla oblongata is a cone-shaped structure of the brain, approximately 3 cm long and 2 cm wide at its largest point.
- The pia mater is a membrane wrapped around the brain and the spinal cord composed of many blood vessels that supply oxygen and nutrients to the nervous tissue of these two cerebral cortex structures.
- The decussation in the medulla oblongata occurs right before the junction between the medulla oblongata and the spinal cord.
- The autonomic functions of the body are the functions that are unconsciously controlled by the body.
- Located in the visual cortex of the brain, the optic chiasm is a decussation that serves as a crossing point of the neural fibers. Thus, the visual field can be distinguished and processed in the corresponding areas of the visual cortex. The name of this tiny structure of the brain comes from the Greek word ‘χίασμα, meaning ‘crossing’ or ‘to mark with X’.
- The descending tracts are the neuron pathways that relay the motor signals from the brain to the lower motor neurons. After receiving the signal, the lower motor neurons directly innervate the muscles in order to produce a movement.
- The medulla oblongata receives its blood supply from the anterior spinal artery, posterior inferior cerebellar artery, as well as from the vertebral artery’s direct branches.
- The medulla oblongata contains both myelinated and unmyelinated nerve fibers.